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RESEARCH INVESTIGATION ON STRAIN ANALYSIS OF METAL SHEETS WITH NOTCHES AND CRACKS
PENNSYLVANIA STATE UNIV UNIVERSITY PARK
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The report presents experimental observations and measurements concerning the strain distribution and changes of the strain distribution at the base of semi-circular notches and at the base of cracks in thin flat metal sheets. The metal sheets were subjected to static and to fluctuating tensile loading. The photoelastic coating method and a method utilizing Newton interference fringes were used to perform the stain observations and measurements. With both methods applied to semi-circular notches, a so-called necking zone could be observed. It was found that the necking zone must have a certain magnitude before cracks are formed at the base of the notch. New details concerning the geometry and magnitude of the strain distribution and its changes were also observed at the base of cracks in thin metal sheets using the interferometric method. To the best of the authors knowledge, this is the first time that this method has been applied to strain analysis around cracks in metal. The residual and total strain distribution, for static loading, at the base of cracks were obtained thusly. Data on the rate of crack propagation and its relationship to the varying areas of permanent deformation around cracks have also been recorded. Author
APPROVED FOR PUBLIC RELEASE